Method of stretch forming rayons



METHOD OF STRETCH FORMING RAYONS Filed Dec. 28, 1964 2 Sheets-"Sheet 1' INVENTORS Phillip W. Esfes AlfrQd R. Johnson AHorney Ga. 37, 2%? P. w. ESTES EITAL 9 METHOD OF STRETCH FORMING RAYONS Filed Dec. 28, 1964 I 2 Sheets-Sheet 2 I50 IT" O -I-I- I% F |4O sv/a I50 :f' 5 50% g 2 g I I- l U) ----IMMERsE0 IN LiQUlD OUT OF LIQUID f, 95% %L|QU|D AMMONIA IN JQX O 1 WATER SOLUTION 0/o I00 I I I I I I TIME, MINUTES I40 L) I? l- I30 U7 ----|MMERSED IN LIQUID NH3/H2O so/Io 2 0UT OF LIQUID II0 ,"i/I I loo .l I I I I TIME, MINUTES I VENTORS Phillip W. Esies vANTI-sci R Johnson Attorney United States Patent Ofiice Patented Oct. 17, 1967 3,347,963 METHOD B3 STRETCH FQRMING RAYONS Phillip W. Estes, Lexington, and Alfred R. Johnson, Reading, Mass, assignors to Arthur D. Little, Inc., Cambridge, Mass, a corporation of Massachusetts Filed Dec. 28, 1964, er. No. 421,449 8 Claims. ((31. 26490) ABSTRACT OF THE DISCLOSURE A method of stretch forming and molding rayon fabrics by which rayon fabrics are subjected to wetting with a liquid ammonia treating agent and forced to conform to a contoured surface to obtain a permanently molded configuration of the fabric.

This invention relates to treating rayon and more particularly to a method of stretch forming rayon fabrics and the resulting formed rayon product.

Woven fabrics are used in many applications where contoured configurations are required. This requirement is generally met by cutting a number of shaped pieces of fabric and sewing them together to obtained the contoured configuration. For example in rayon textile clothing items such as brassieres, innerlinings for coats and suits and certain types of gloves, contoured configurations are obtained in this manner. The need for contoured fabric products also arises in the construction of upholstery and automobile seat covers where cutting and sewing are the normal method of forming these items. Another application for a contoured fabric is in the construction of cone shapes for hi-fi speaker systems.

The need for cutting of a number of shaped pieces and for sewing them together adds materially to the cost of such items. Moreover, the finished product is not completely smooth because of the presence of the seams. It would therefore be desirable to be able to mold a fabric to the desired configuration and thus eliminate cutting a number of pieces and sewing them together. We have found that it is possible to stretch form rayon fabrics which has been treated with liquid ammonia to a desired configuration and thus overcome the added work and expense of the sewing together of a number of different pieces.

Rayon fabrics are available in quantity and at reasonable cost and these rayon fabrics may be so made that they possess a variety of physical properties. The term rayon as hereinafter used is meant to include all of the regenerated cellulose materials whether formed by the well-known viscose or cuprammonium processes. The rayon fabrics may be woven of spun or continuous filament yarns. The term is also meant to include the recently developed high-modulus or polynosic rayons. The various cellulose acetates are sometimes classed with the rayons and the term as used hereinafter is also meant to include those cellulose acetates which are not degraded by liquid ammonia.

Rayons as defined and as the term is used herein cannot be subjected to some of the treatments which are commonly applied to other cellulosic materials, in particular to the cottons. For example, it has not been possible to mercerize rayons (except the polynosic rayons) with sodium hydroxide. Rather than swell in sodium hydroxide as cotton does, most rayons disintegrate. However, rayon fabrics may be treated with liquid ammonia without sustaining any determinable damage, and while wet with liquid ammonia they may be stretch formed into perma nent contoured configurations.

It is therefore a primary object of this invention to provide a method of stretch forming rayon fabrics into a permanent configuration. It is another object of this invention to provide such a method which permits extending rayon fabrics to as much as 70 or and thus to form relatively deep drawn contoured configurations. It is another object of this invention to provide a method of forming rayon into permanent configurations which may be subjected to machine laundering without loosing any appreciable amount of the contour acquired through stretch forming. It is another object of this invention to provide a method for making contoured rayon fabric articles without cutting and sewing. It is yet another object of this invention to provide a method of stretching rayon while at the same time increasing the tensile strength of the rayon yarn on a cross-sectional area basis. It is another primary object of this invention to provide stretch formed rayon articles for a variety of uses including clothing and upholstery. Other objects of the invention will in part be obvious and will in part be apparent hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others and the article possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosures, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawings in which FIG. 1 illustrates the apparatus used to evaluate stretch in a rayon yarn;

FIG. 2 is a plot of time vs. percent permanent srtetch of rayon yarn treated with various concentrations of liquid ammonia-water mixtures;

FIG. 3 is a plot of time vs. permanent stretch for rayon yarn treated with liquid ammonia containing 10% by weight water;

FIGS. 47 illustrate the steps of one molding technique which may be applied in stretch forming rayon in accordance with the method of this invention; and

FIGS 8-11 illustrate the steps of another stretch forming technique applicable to the method of this invention.

In stretch forming rayon fabric in accordance with this invention the fabric is treated with liquid ammonia and, while at least a portion of the ammonia is in the rayon, tension is applied to stretch the fabric into the desired contoured configuration. Various modifications of the method will be described in detail.

In the following detailed description of this invention the term liquid ammonia is used to include anhydrous liquid ammonia which has a boiling point of 33.35 C., and solutions of liquid ammonia in which there is present an appreciable amount of free ammonia, NH in a liquid state. Thus, the ammonia may be in solution with water, the lower aliphatic alcohols, polyhydric alcohols, ethers and other suitable solvents. These solutions will of course vary in temperature and effectiveness depending upon their composition and the equilibrium conditions which prevail.

The conditions under which the rayon is treated can be first presented in terms of stretching rayon yarn; and subsequent to this description of the treating conditions, examples of stretch forming rayon fabrics will be given.

During a portion of the stretch time it is necessary to be able to expose the rayon to the liquid ammonia treating liquid. Since anhydrous liquid ammonia at atmospheric pressure has a boiling point of -33.4 C., the treating liquid was conveniently contained in a Dewar flask. Since stretching was found to take place both in and out of the liquid ammonia, an apparatus was constructed to permit tension to be continuously applied while the liquid am monia could contact the rayon yarn sample and then be removed without disturbing its condition under tension. The test apparatus thus devised to perform these evaluations is illustrated in FIG. 1. A loop of rayon yarn Was affixed in notches to be held taut by two steel rods 11 and 12. fastened to be movable with respect to each other near one end at a pivot point '15. Rod 11 was held in a fixed position by means of a suitable clamp 16 while rod 12 was free to move and exert tension on loop 10. That portion of the ends of the rods 11 and 12 Which held the rayon yarn sample 10 could be immersed in the liquid ammonia treating liquid by bringing a Dewar flask 17 containing theliquid 18 up into position to completely immerse the rayon yarn. Tension was applied to the rayon yarn loop 10 by attaching to movable rod 12 a line 20 on the end of which was a weight 21 and which was held in position and guided by means of a pulley 22. By measuring the distance, d, between the steel rods at selected points a measurement of the amount of stretching experienced by the rayon yarn sample 10 was obtained. The rayon yarn which was used for the preliminary evaluations was a 1860 denier/ 1500 filament rayon tire yarn. It was found that this yarn would break under a tension of about 1700 grams. When the yarn was immersed in the liquid ammonia the breaking strength was approximately 500 grams, a fact that led to the choice of an arbitrary weight of 280 grams which was applied during the stretching period.

In making determinations of the amount of stretch using the apparatus shown in FIG. 1 it was found that stretching took place while the yarn was immersed in the liquid ammonia as well as after the yarn had been withdrawn from the liquid ammonia treating liquid. FIG. 2 is a plot of time vs. percent stretch using anhydrous liquid ammonia and various concentrations of liquid ammoniawater solutions. Despite the normal temperature of liquid ammonia, water may be added to it without freezing. Equilibrium conditions are such that even when 50% of the liquid ammonia treating liquid is water, there remains an appreciable quantity (i.e., from 10 to 20%) f free liquid ammonia in the solution.

In the plots of FIG. 2 the dotted line portions of each curve represent the times that the rayon yarn was immersed in the treating liquid and the solid line portions represent the time periods over which the yarn was exposed to the atmosphere. In each of the cases plotted in FIG. 2 tension was applied immediately and some stretching took place during the initial immersion of the yarn in the liquid ammonia. This stretching continued when the liquid ammonia bath was removed and, after a subsequent immersion, was continued when the yarn was again removed from the liquid ammonia. Each curve, however, levels ofl after several immersions and a limit to the extent to which the rayon yarn can be stretched is reached. In the case of liquid ammonia containing 10% by weight water the amount of stretching is greater and the rate of stretching after removal from the liquid ammonia is more rapid for the conditions under which these data were obtained than when anhydrousliq-uid ammonia was used.

FIG. 2 illustrates that the amount of water added to the liquid ammonia may vary from zero to as much as 50% by weight of the total treating liquid, with 30% water being a preferable upper limit. Although the 10% by weight water mixture producesthe greatest percentage of stretching with two immersions under these conditions, the 30% by weight water mixture achieves the maximum rate of stretch during the first immersion under these same conditions. However, subsequent immersions do not increase the. overall extent of stretching using this liquid mixture. If rapid stretching with a single immersion or treatment with the liquid is desired at the expense of overall percentage of stretching to form the molded rayon product, then it may be desirable to use :a treating liquid which has an appreciable percentage of water mixed with the liquid ammonia. The method of this invention therefore altords flexibility of operation.

The reasons why the presence of water enhances the action of the liquid ammonia and why stretching continues after the yarn has been removed from the treating liquid are not completely understood. The following is offered, however, as a possible explanation for these two unexpected effects. The liquid ammonia is apparently a swelling agent for the cellulose of the rayon and it is possible that intracrystalline swelling is optimized in the presence of some water. This intraorystalline swelling in turn produces a structure within the fibers which makes stretch forming possible. When anhydrous liquid ammonia is used, it is possible that these optimum conditions are not reached, or that they are only approximated with multiple treatments. Moreover, when anhydrous liquid ammonia is used and the rayon is withdrawn from the liquid it is possible that elongation or stretching is inhibited by the tendency of the cellulose structure to recrystallize under the tension of stretch forming. The presence of water molecules in the ammonia cellulose may promote a structure which, upon orientation by stretching, results in either less crystallization or more probably in retardation of the rate of recrystallization, thus permitting the fibers to be more highly elongated under a given pressure. This last postulation would partially explain why stretch forming is continued during drying after the yarn has been removed from the treating liquid.

It is well-known that cellulosic materials including r-ayons normally contain some moisture which is more or less in equilibrium with the moisture in the normal atmosphere. Thus the regenerated celluloses which make up the rayons typically contain about 12% moisture in normal atmospheres. Samples of the rayon yarn were therefore heated to essentially complete dryness and evaluated for stretching in the manner described. Little if any difference in stretching was noted for the dry rayon when compared with a rayon yarn which had been exposed to the normal atmosphere over an extended period of time. However, when water-soaked rayon was evaluated (for stretching it was found that neither the extent of stretching nor the rapidity with which it could be accomplished was equal to the dry yarn or that in which the moisture Was in equilibrium with the atmosphere.

FIG. 3 illustrates two ways in which the -10 mixture of liquid ammonia and water may be employed in the stretch forming method of this invention. Curve 1 is a stretch curve for rayon yarn which was permitted to remain in the ammonia solution for 5 minutes before any tension was applied. The dotted portion of this curve (which represents immersion in the liquid ammonia) shows that, under the conditions employed, after a brief residence time in the liquid ammonia the applicationof tension resulted in immediate stretching of the yarn and after removal from the bath stretching continued at a very rapidrate until the yarn had reached a length which was equivalent to about 168% of its original length; Curve 2 shows that under the same conditions when tension is applied simultaneously with immersion in the liquid ammonia bath stretching begins immediately but proceeds less rapidly; and after removal from the bath the stretching levels off at a value whichis somewhat below that shown in curve 1. Are-immersion and subsequent withdrawal permits further stretching and the process can be repeated until the yarn has been stretched to the same extent as it was in the case of curve 1. A short residence time in the liquid ammonia bath up to 5 minutes prior to the application of tension may be preferable under some conditions inasmuch as it can permit the more rapid application of molding pressures and the attainment of the molded configuration in less time. Thus FIG. 3 illustrates that it is possible to mold rayon in a matter of 5-10 minutes and that one thorough exposure to the liquid ammonia under these conditions is sutficient.

Although we do not wish to be bound by any one explanation for the improved stretching performance for rayon when a short soaking period is employed, it would seem that perhaps a short residence in the'treating liquid in the absence of tension or pressure permits the liquid to enter the fibers more thoroughly than when tension is applied.

The rayor yarn prior to treatment and stretching had an average breaking or tensile strength of about 1700 grams. The stretched yarn after drying had an average tensile strength of about 1300 grams which at first would indicate a drop of about 18%. However, if it is assumed that the density of the yarn is unchanged with treatment, it can be shown that an increase in the length of the yarn of 60% results in a decrease in the diameter of 37.5%. Thus the tensile strength when calculated for a unit crosssectional area was actually increased in the stretching treatment by about 22%.

Microscopic examinations of the untreated and of the stretched rayon yarns indicated that the stretched yarn had a somewhat smoother surface. Some necking down of the individual filaments was noticeable, apparently because the filament stretched more in some sections than in others.

The stretching of the rayon yarn indicated the conditions under which rayon fabric formed of this yarn can be retch formed into various permanent configurations. Many techniques for stretch forming thin flat sheet materials are known and two of these are illustrated in FIGS. 47 and 81 l.

In FIGS. 4-7 one technique for stretch forming rayon fabric in accordance with the method of this invention is diagrammatically illustrated step by step. The rayon fabric 25 is held firmly in place by means of any suitable holding means such as by the pair of jaws 26 illustrated in FIG. 4. In the technique shown in FIGS. 4-7 the liquid treating material (e.g., a mixture of 90% liquid ammonia and water) is applied to one surface of the rayon fabric 25 through suitable nozzles 27 which cause a stream 28 of the liquid treating agent to impinge on the surface of the fabric and to thoroughly wet it with the treating agent. Either simulaneously with the application of the liquid treating agent or after a few minutes soaking therewith, a male mold form 29 is forced down with pressure to contact the fabric thus applying tension to fabric 25 stretching it. The application of the liquid treating agent may be continued, as shown in FIG. 5 with the contacting of the mold with the fabric. Alternatively, the liquid treating agent may be shut off and then turned on again depending upon the type of stretching of the fabric which is desired. This will be carried out of conform with a desired stretching and forming cycle as indicated in FIGS. 2 and 3. FIG 6 illustrates the attainment of the final stretch forming. Subsequent to this the mold form is removed and their results a contoured rayon fabric 30 as shown in FIG. 7. The configuration imparted to the rayon fabric is permanent and the article may be washed without destroying the permanent configuration thus imparted to the rayon fabric.

As an alternative to applying the liquid treating agent by spraying, the assembly consisting of the rayon fabric 25 and its holding means 26 may be immersed in a bath of the treating liquid and the mold 29 may be pressed down onto the fabric either while it is immersed in the liquid, after it is removed therefrom, or continuously during treating and after removal from the liquid. Application of the mold to the fabric surface may take place simultaneously with its immersion into such a liquid treating bath or it may be subsequent to immersion in accordance with the preferred embodiment of the method which, as shown in FIG. 3, comprises permitting the fabric to be thoroughly soaked in the liquid prior to the application of tension through pressure thereon.

FIGS. 8-11 illustrate the use of well-known vacuum forming technique to the method of stretch forming rayon fabric according to this invention. In this modification there is provided a mold form 32 having perforations 33 and a flange 34, the latter serving along with suitable auxiliary holding means 35 to clamp the rayon fabric 25 into position. In accordance with vacuum forming techniques, there is provided a vacuum chamber 36, along.

with a line 37 controlled by valve 38, which leads to a.

vacuum pump not shown. The liquid treating agent is applied to the topsurface of the fabric 25 by any suitable distribution means such as spray head 39 which is supplied through line 40- and which serves to distribute the liquid treating agent 41 over the surface of the fabric. Subsequent to the thorough wetting of the rayon fabric with the treating agent, a gas impermeable membrane such as a flexible rubber sheet 44 is placed on the top surface of the fabric 25, valve 38 is opened (FIG. 9) and a vacuum is produced within housing 36 thus forcing the rayon fabric to conform to the surface of the mold 32 and applying the required tension thereto. With the completion of the forming step as shown in FIG. 10, the fabric is removed to form a contoured rayon article 30 as shown in FIG. 11. Because of the nature of the vacuum forming technique, as illustrated somewhat diagrammatically in FIGS. 8-10, it is preferable to use a liquid treating agent which achieves the maximum amount of stretch with a single immersion and in the shortest amount of time. Thus if the stretch forming is carried out under conditions similar to those under which the data of FIG. 2 were obtained, a treating liquid which was a mixture of about 70% liquid ammonia and 30% water would be preferable. The optimum composition of the liquid treating agent will depend upon the stretch forming techniques used, the rayon fabric being so formed and the conditions under which it is desired to perform the stretch forming.

An apparatus essentially equivalent to that illustrated in FIG. 4 was used to stretch form rayon fabric shapes, except that the fabric was wetted by pouring the liquid treating agent on the fabric from above and then moving the mold 29 downwardly. This was done in steps, i.e., after the fabric was partly stretch molded as indicated in FIG. 5 the mold was removed and an additional quantity of liquid treating agent was applied and then the mold was again forced against the fabric surface. Various rayon fabrics were used and they included a 150 denier, 60 filament x 60 viscose rayon griege goods, a spun rayon viscose challis, and a spun Avril fabric manufactured by Testfabrics, Inc. The method of stretch forming was equally applicable to fabrics formed of both filament and spun rayon yarns.

It was possible in stretch forming the rayon fabric in this example to increase the fabric area by as much as or more. As noted above laundering the contoured rayon fabric in an automatic washing machine using detergents did not destroy the shape or contour or decrease the area of the contoured fabric. After the stretch forming the fabric was somewhat stiff but laundering removed much of this stiffness.

It will be seen from the above description and examples that there is provided by this invention a method of stretch molding rayon fabric to give contoured configurations which are permanent. Such molded rayon fabrics have a wide variety of uses as noted above and the method of this invention provides a way of making contoured rayon fabric articles without the customary cutting and sewing which is expensive and time-consuming. Moreover, the finished article is free from seams and may be made in many intricate shapes and configurations.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in carrying out the above method and in the article set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which as a matter of language might be said to fall therebetween.

We claim: 1. A method of imparting a permanent contoured configuration to rayon fabrics, comprising the steps of (a) wetting rayon fabric with a liquid ammonia treating agent; and Y (b) forcing the treated rayon fabric to conform to the contoured surface of a form while said rayon fabric is Wet with said treating agent, whereby said fabric acquires the contour of said surface.

2. A method in accordance with claim 1 wherein said forcing said treated rayonfabric to conform to said contoured surface comprises forcing said form under pressure against said-treated rayon fabric.

3. A method in accordance with claim 1 wherein said forcing said treated rayon fabric to conform to said contoured surface comprises the step of establishing a pressure differential on the two sides of a foraminous mold form to cause said treated rayon fabric to contact the surface of said mold form and assume its configuration.

4. A method in accordance with claim 1 wherein steps (a) and (b) are performed serially.

5. A method in'accordance withclaim 1 wherein steps (a) and (b) are performed substantially simultaneously.

6. A method in accordance with claim 1 wherein steps (a) and (b) are repeated at least twice.

7. A method in accordance with claim 1 wherein said treating liquid is an aqueous solution of liquid ammonia containing up to about Water by weight.

8. A method in accordance with claim 4 wherein said wetting said rayon fabric is continued up to about 5 minutes before said fabric is forced to conform to said contoured surface of said form.

References Cited UNITED STATES PATENTS 4/1935 Mahn -8 8/1938 Pratt 125-8 

1. A METHOD FOR IMPARTING A PERMANENT CONTOURED CONFIGURATION TO RAYON FABRICS, COMPRISING THE STEPS OF (A) WETTING RAYON FABRIC WITH A LIQUID AMMONIA TREATING AGENT; AND (B) FORCING THE TREATED RAYON FABRIC TO CONFORM TO THE CONTOURED SURFACE OF A FORM WHILE SAID RAYON FABRIC IS WET WITH SAID TREATING AGENT, WHEREBY SAID FABRIC ACQUIRES THE CONTOUR OF SAID SURFACE. 